1. Field of the Invention
This invention relates generally to slide fasteners and more particularly to such slide fasteners as are suitable for fluid-tight applications.
2. Description of the Prior Art
There have been proposed numerous types of fluid-tight slide fasteners for use on for example diving suits, water rescue equipment and other articles requiring hermetic seal against fluid leakage.
A typical known fluid-tight slide fastener is disclosed in Japanese Patent Publication No. 35-9296published July 15, 1960. The disclosed slide fastener comprises a pair of stringers each having a water-proof support tape and a row of coupling elements mounted on one longitudinal edge of the tape, the stringers being coupled and uncoupled by a slider. To establish fluid-tightness of the slide fastener, the longitudinal edge of the support tape is bent perpendicularly to the general plane of the slide fastener and includes an intermediate portion folded around the row of elements. The thus folded tape edge is externally enveloped by a row of sealing clamps positioned in registry with the corresponding individual coupling elements. The fastener stringers are joined together at their upper ends where a top end stop is disposed to limit movement of the slider. The slide fastener further includes a backing sheet adhered to the underside of the upper end portions of the support tapes. The backing sheet includes a tapered sealing projection projecting into a space between the bent longitudinal tape edges, the projection being spaced a distance from the top end stop. As the slider is moved toward the top end stop to close the slide fastener, the two rows of coupling elements are progressively coupled together and the bent longitudinal edges are brought into sealing engagement with each other. When the slide fastener is fully closed, several coupling elements, which are disposed between the top end stop and the sealing projection, are left uncoupled. However, the sealing projection is held in sealing contact with a lower sealing abutment of each bent longitudinal tape edge so that the slide fastener is kept water-tight as a whole.
The known slide fastener of the foregoing construction has the following disadvantages: As the bent longitudinal edges of the opposed support tapes are parallel spaced from one another by a distance smaller than the width of a wedge or diamond of the slider, a muscle effort is required to move the slider to its uppermost position against the frictional resistance acting between the longitudinal tape edges and the slider diamond. The lower sealing abutments of the longitudinal tape edges are spread by the sealing projection. When the slider passes over the sealing projection, the thus spread tape edge portions are brought into severe frictional engagement with opposite side flanges of the slider. Due to this undue friction, the slider is likely to stop ahead of the top end stop and hence it is not possible to fully close the slide fastener. These difficulties have been confirmed through an experiment which was carried out in respect of the slide fasteners made in accordance with the above-mentioned Japanese publication and available in the market.